WKP PFS – Geotechnical Section Approved by: Approval Date: TBA OceanaGold PEX-000-PLN-046-A Page 8 of 22 1.5.2 Uniaxial Compressive Strength All rock testing has been done at the E-Precision laboratory in Perth, Australia. Table 7 shows the rock density and UCS values measured for the 11 lab samples that were tested. The samples were taken from various lithologies including Andesite Flow, Eastern Rhyolite Flow, and Northern Rhyolite Flow. The lithologies that is most relevant for the WKP mine design in the PFS are the Eastern Rhyolite Flow and Northern Rhyolite Flow. The sample diameters range from 45mm to 83mm. The UCS values have been normalized to a standard 50mm diameter using the standard empirical formula: σc50 = σc / (50/D) 0.18 (Equation 3) Table 7: UCS results for WKP rock There are large variations in the UCS values even within the same lithology. Andesite ranges from 47 to 123 MPa. Northern Rhyolite ranges from 138 to 191 MPa. Eastern Rhyolite ranges from 15 to 238 MPa. The large variation in the UCS implies that the sample population is too small, and more UCS testing will be required to understand this important geotechnical parameter. In the Scoping Study (SRK, 2019). The point load testing data was analysed in order to make up for the lack of UCS testing. However, point load testing (PLT) is also subject to a lot of variation, and its correlation with UCS is not reliable. For example, Sample WKP2020RP-006 has a UCS of 123 MPa and a PLT value of 3.76. Sample WKP2020RP-002 has a UCS of 47 MPa and a PLT value of 4.9. The relationship between the UCS and the PLT described in the Scoping Study was as follows: UCS=17.4*PLT (Equation 4) This equation would have predicted a UCS value of 65 MPa for Sample-006, and 85 MPa for Sample-002. Another way to estimate the UCS of a rock sample is to use the relationship with rock density. Figure 6 shows that the relationship between the rock density and the UCS for the eight samples of rhyolite UCS=1170*ln(ρ) – 880 (Equation 5) However, the data shows that the density-UCS relationship can be unreliable for rock densities less than 2.35. The WKP density database shows that the 1st quartile is 2.44, and the 2nd quartile is 2.5. Therefore, Equation 5 would predict that the 1st quartile UCS is 164 MPa.
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